The invention relates to spray pyrolysis, which involves forming a film by spraying onto a heated substrate an atomized solution containing the appropriate salts of the constituent elements (e.g., Te) of the film compound. The chemical reaction occurs upon spraying on the heated substrate, and the nonconstituent elements of the salts are removed by volatilization along with the solvent, typically water. For example, U.S. Pat. No. 3,148,084 discloses, along with other examples, the formation of CdS by spray pyrolysis according to the following equation: ##STR1## The resistivity of the film is then lowered by a post-deposition annealing step.
Before the conception of the invention claimed herein, Messrs. Steven A. Lis and Harvey B. Serreze proposed using H.sub.2 in the ambient gas and/or spray gas to act as a reducing agent to convert impurities to a volatile form and to also allow the use of Te in a different oxidation state in the starting material than it is in the film. Our attempts to implement that proposal were unsuccessful.